Boundary tracking control module for rotary steerable systems

ABSTRACT

A rotary steerable bottom hole assembly includes a drill bit disposed at a distal end thereof, and azimuthal resistivity antennas and electronics configured to measure a distance to a formation boundary.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. § 120 as a continuationof U.S. application Ser. No. 16/126,485, filed on Sep. 10, 2018 which isa continuation of U.S. application Ser. No. 15/937,459, filed on Mar.27, 2018 and allowed on Aug. 8, 2018, which is a continuation-in-part ofU.S. application Ser. No. 15/920,034 filed Mar. 13, 2018, which is acontinuation of U.S. Pat. No. 9,952,347 filed Sep. 6, 2017, which is acontinuation of U.S. Pat. No. 9,767,153 filed Mar. 22, 2017, which is acontinuation of U.S. Pat. No. 9,645,276 filed Jan. 12, 2016, which is acontinuation of U.S. Pat. No. 9,268,053 filed Jun. 12, 2014, whichclaims priority to U.S. Provisional Application No. 61/834,272 filedJun. 12, 2013, all of which are hereby incorporated by reference intheir entireties.

FIELD

Embodiments disclosed herein relate to rotary steerable systems. Moreparticularly, embodiments disclosed herein relate to a boundary trackingcontrol module for rotary steerable systems.

BACKGROUND

Directional drilling is a method of controlling the direction anddeviation of a wellbore to reach a pre-determined underground target orlocation. This may be accomplished in a number of ways including throughthe use of whipstocks, bottom hole assembly configurations, instrumentsto measure the path of the wellbore in three-dimensional space, datalinks to communicate measurements taken downhole to the surface, mudmotors and special BHA components, including rotary steerable systems,and drill bits.

FIG. 1 illustrates a conventional rotary steerable system used indrilling an extended horizontal section. The conventional rotarysteerable bottom hole assembly (“BHA”) may include a drill bit (1), arotary steerable system (2), a stabilizer (3), apulser/battery/electromagnetic (“EM”) transmitter (4), a mud motor (5),a measurement-while-drilling (“MWD”) tool (6), heavy wall drill pipe(7), and a drill collar (8). FIG. 2 illustrates a perspective view of aconventional rotary steerable system (“RSS”) (9). The RSS (9) includeshydraulic rams (10) that are radially extendable outward to pressagainst the wellbore thereby causing the drill bit (1) to press on theopposite side causing a direction change. The RSS (9) may also include ashort hop transmitter gap (11) and receiver gap (12). A bit box (13) maybe disposed between the drill bit (1) and the RSS (9). However, there isstill need for an improved RSS.

SUMMARY OF THE INVENTION

In one aspect, embodiments disclosed herein relate to a rotary steerablebottom hole assembly including a drill bit disposed at a distal endthereof and azimuthal resistivity antennas and electronics configured tomeasure a distance to a formation boundary. The azimuthal resistivityantennas include an axial antenna including a wire winding forgenerating an axial magnetic moment parallel with the longitudinal axis,and a transverse antenna including an antenna body having a longer axisdisposed longitudinally in the housing, and a wire coil having a centralaxis disposed around the antenna body, wherein the wire coil centralaxis is substantially perpendicular to the longer axis of the antennabody, and wherein the wire coil is configured to generate a transversemagnetic moment orthogonal to the housing longitudinal axis.

In another aspect, embodiments disclosed herein relate to a rotarysteerable system including azimuthal resistivity antennas andelectronics configured to measure a distance to a formation boundary.The azimuthal resistivity antennas include an axial antenna including awire winding for generating an axial magnetic moment parallel with thelongitudinal axis and a transverse antenna including an antenna bodyhaving a longer axis disposed longitudinally in the housing, and a wirecoil having a central axis disposed around the antenna body, wherein thewire coil central axis is substantially perpendicular to the longer axisof the antenna body, and wherein the wire coil is configured to generatea transverse magnetic moment orthogonal to the housing longitudinalaxis.

In yet another aspect, embodiments disclosed herein relate to a methodof directional drilling including measuring a distance between a housingand a formation boundary with azimuthal resistivity antennas comprisingan axial antenna including a wire winding for generating an axialmagnetic moment parallel with the longitudinal axis, and a transverseantenna including an antenna body having a longer axis disposedlongitudinally in the housing, and a wire coil having a central axisdisposed around the antenna body, wherein the wire coil central axis issubstantially perpendicular to the longer axis of the antenna body, andwherein the wire coil is configured to generate a transverse magneticmoment orthogonal to the housing longitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the accompanying drawings wherein,

FIG. 1 illustrates a conventional rotary steerable bottom hole assemblyused in directional drilling an extended horizontal section.

FIG. 2 illustrates a perspective view of a conventional rotary steerablebottom hole assembly.

FIG. 3 illustrates a perspective view of an embodiment of an improvedrotary steerable bottom hole assembly.

FIG. 4a illustrates an enlarged perspective view of the improved rotarysteerable system of FIG. 3.

FIG. 4b illustrates an enlarged perspective cutaway view of the improvedrotary steerable system of FIG. 4 a.

FIGS. 5A-5C illustrate embodiments of azimuthal resistivity measurementantennas having a transverse elemental antenna.

FIGS. 6A-6B illustrate embodiments of azimuthal resistivity measurementantennas having multiple azimuthally-spaced transverse elementalantennas.

FIG. 7 illustrates an embodiment of transverse elemental antennacomponents.

FIGS. 8A-8D illustrate embodiments of composite transverse antennaconfigurations.

FIG. 9 illustrates an embodiment of axial antenna components.

FIGS. 10A-10C illustrate embodiments of co-located antennas.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to an improved rotary steerablesystem (“RSS”) for directional drilling. More particularly, embodimentsdisclosed herein relate to a boundary tracking control module that isintegrated within a RSS. The rotary steerable BHA may include a drillbit, a RSS housing, a stabilizer, a pulser/battery/electromagnetic(“EM”) transmitter, a mud motor, and a measurement-while-drilling(“MWD”) tool, and other components such as drill pipe or drill collarsdisposed above.

The RSS housing may be disposed between a drill bit and a stabilizer.The RSS housing may include one or multiple hydraulic pistons and ramsarranged around a circumference of the housing. The pistons and rams areradially extendable inward and outward by a hydraulic pump and pumpdrive, enclosed within the RSS housing, to press against the wellborethereby causing the drill bit to press on the opposite side of thewellbore causing the drill bit to change the wellbore direction. Thisconfiguration is known in the industry as “push-the-bit”. However, itshould be understood that embodiments disclosed herein for an improvedRSS may also be employed in “point-the-bit” configuration, which arealso known and understood. In certain embodiments, the RSS housing doesnot rotate at all, i.e., zero (0) revolutions per hour. In otherembodiments, the RSS may be “non-rotating”, which includes not rotatingat all, but also includes rotating very slowly. For example,“non-rotating”, as used herein, may include rotating at less than five(5) revolutions per hour, or less than ten (10) revolutions per hour, orless than fifteen (15) revolutions per hour, or less than twenty (20)revolutions per hour, or less than twenty five (25) revolutions perhour, or less than thirty (30) revolutions per hour, or less than forty(40) revolutions per hour. “Non-rotating” may also include rotating muchslower relative to “rotating” components, such as those components fromthe surface down to the mud motor, e.g., drill pipe. “Rotating”, as usedherein, for components from the surface down to the mud motor mayinclude rotating at or greater than 1,000 revolutions per hour, orgreater than 1,500 revolutions per hour, or greater than 2,000revolutions per hour, or greater than 3,000 revolutions per hour, orgreater than 4,000 revolutions per hour, or greater than 5,000revolutions per hour, or greater than 6,000 revolutions per hour.“Rotating”, as used herein, for components from the mud motor down tothe drill bit, e.g., stabilizer and drill bit, may include rotating atgreater than 15,000 revolutions per hour, or greater than 20,000revolutions per hour, or greater than 25,000 revolutions per hour, orgreater than 30,000 revolutions per hour.

The RSS housing encloses azimuthal resistivity measurement antennas,which may be either transmitting or receiving antennas, of which theremay be any number in any antenna placement or arrangement. The azimuthalresistivity antennas are configured to provide imaging capabilities ofthe surrounding formation, including formation boundaries, withoutrotating. For example, azimuthal resistivity antennas capable of imagingwithout rotating may be those described in U.S. Pat. No 9,767,153, U.S.Pat. No. 9,645,276, U.S. Pat. No. 9,268,053, and U.S. Publication No.2017/0371063, all of which are assigned to the same assignee, and herebyincorporated herein by reference in their entireties. Any other antennascapable of azimuthal resistivity measurements in a non-rotating mode maybe used in accordance with embodiments disclosed herein.

The RSS housing also encloses an azimuthal resistivity measurementantenna electronics, also referred to herein as “measurementelectronics.” The measurement electronics control and operate theazimuthal resistivity antennas for making measurements of thesurrounding formation, including formation boundaries. The RSS alsoencloses azimuthal resistivity measurement antenna tuning electronicsthat are configured to condition antenna signals to make sure theantennas are measuring properly, e.g., calibration.

The RSS housing also encloses a control module. The control module maybe any type of microprocessor unit (“MPU”) or module which incorporatesthe functions of all central processing for the rotary steerable systemon a single integrated circuit (“IC”), or at most a few integratedcircuits. The control module may be a multipurpose, clock driven,register based, digital-integrated circuit which accepts binary data asinput, processes it according to instructions stored in its memory, andprovides results as output.

The control module of embodiments disclosed herein may be configured toexecute a pre-programmed well trajectory, e.g., a three-dimensional“well plan” or path, or may execute commands from the MWD devicedownlinked from the surface. For example, the control module may beconfigured to execute a pre-programmed well trajectory which includesazimuth (or direction), which is the angle in degrees between ahorizontal component of a wellbore axis and the reference north (theazimuth value varies from 0 degrees to 360 degrees in a clock-wisedirection; north is represented as 0 degrees or 360 degrees; east as 90degrees; south as 180 degrees; west as 270 degrees), and total verticaldepth (“TVD”). This may be referred to as a “geometric setting.”

In addition, the control module of embodiments disclosed herein may bepre-programmed to maintain a certain or desired distance between acenterline of a rotary steerable system and a formation boundary aboveor below the rotary steerable system. This may be referred to as a“boundary tracking setting.” The control module may be pre-preprogrammedwith a full well trajectory and the boundary tracking setting preventsthe drill bit from exiting the desired formation if an upper or lowerboundary turns out to be in a slightly different location. That is, thecontrol module is configured to control a vertical component of thethree-dimensional well path to avoid exiting from the formation, or adesired portion of the formation, either through a top or bottom of theformation. To do so, the azimuthal measurement antennas “track theboundaries” for the formation above or below by determining the distanceto a boundary when close to it. For example, the azimuthal measurementantennas may determine the distance when within less than five feet, orless than four feet, or less than three feet, or less than two feet, orless than one foot from a boundary. Upon detecting that the rotarysteerable system is about to exit through a formation boundary, or istoo close to a formation boundary (e.g., less than a certain or desireddistance), the control module corrects the rotary steerable system path.

Accordingly, once the geometric and boundary tracking settings arepre-programmed, the control module acts autonomously in responding tothe changing geology of a formation, much like a self-driving vehicle.As the rotary steerable system is travelling along a pre-programmedazimuth (or direction), the azimuthal resistivity measurement antennasare measuring its distance from formation boundaries above or below, andbased on the measurements, the control module is determining whethercorrection up or down is needed to avoid exiting the formation. Thus,the control module steers the rotary steerable system to stay within theproducing formation and/or reach a pre-determined target or location inthe formation.

Boundary tracking data may be based on a tool face (“TF”) angle obtainedby the control module. In certain embodiments, if the azimuthalresistivity measurement antennas require their own tool face sampling,the tool face angle at the control module may be corrected by enteringan angle value for the radial offset between the control module and themeasurement electronics. The control module is configured to measure TFangle and, if necessary, to make corrections to inclination or azimuth.The control module may be configured to communicate with thepulser/battery/electromagnetic (“EM”) transmitter and/or the MWD tool.In certain embodiments, the control module and the measurementelectronics may be axially aligned to avoid making a tool face offsetcorrection. For example, the control module and the measurementelectronics may be hard mounted on the same platform within thenon-rotating RSS such that they are axially aligned.

FIG. 3 illustrates a perspective view of an embodiment of a system withan improved boundary tracking control module disposed in a rotarysteerable system. The rotary steerable system may include a drill bit(1) of any type, the RSS housing or section (14) having the boundarytracking control module within, a stabilizer (3) of any type, apulser/battery/electromagnetic (“EM”) transmitter (4), a mud motor (5)of any type, and a measurement-while-drilling (“MWD”) tool (6) of anytype, and other components such as drill pipe or drill collars shown inFIG. 1 disposed above. FIGS. 4a and 4b illustrate, respectively, aperspective view and cutaway view of an embodiment of an improved RSS(14). The RSS housing (14) includes hydraulic rams (10) that areradially extendable inward and outward by a hydraulic pump (19) and pumpdrive (20)—both enclosed within RSS (14)—to press against the wellborethereby causing the drill bit (1) to press on the opposite side of thewellbore and cause a direction change, i.e., “push-the-bit”.

The RSS housing (14) is disposed between the drill bit (1) and thestabilizer (3). In certain embodiments, the RSS (14) does not rotate atall, i.e., zero (0) revolutions per hour. In other embodiments, the RSS(14) may be “non-rotating”, which includes not rotating at all, but alsoincludes rotating very slowly. For example, “non-rotating”, as usedherein, may include rotating at less than five (5) revolutions per hour,or less than ten (10) revolutions per hour, or less than fifteen (15)revolutions per hour, or less than twenty (20) revolutions per hour, orless than twenty five (25) revolutions per hour, or less than thirty(30) revolutions per hour, or less than forty (40) revolutions per hour.“Non-rotating” may also include rotating much slower relative to“rotating” components, such as the drill bit, stabilizer, drill pipe,and others. “Rotating”, as used herein, for components from the surfacedown to the mud motor may include rotating at or greater than 1,000revolutions per hour, or greater than 1,500 revolutions per hour, orgreater than 2,000 revolutions per hour, or greater than 3,000revolutions per hour, or greater than 4,000 revolutions per hour, orgreater than 5,000 revolutions per hour, or greater than 6,000revolutions per hour. “Rotating”, as used herein, for components fromthe mud motor down to the drill bit, e.g., stabilizer and drill bit, mayinclude rotating at greater than 15,000 revolutions per hour, or greaterthan 20,000 revolutions per hour, or greater than 25,000 revolutions perhour, or greater than 30,000 revolutions per hour.

The RSS housing (14) encloses azimuthal resistivity measurement antennas(15), (16), and (17), which though illustrated in a particulararrangement with three shown, may be transmitting or receiving antennasin any number, e.g., greater than or less than three, and in any antennaplacement or arrangement. The azimuthal resistivity antennas (15)-(17)are configured to provide imaging capabilities of the surroundingformation without rotating. For example, azimuthal resistivity antennascapable of imaging without rotating may be those described in U.S. Pat.No 9,767,153, U.S. Pat. No. 9,645,276, U.S. Pat. No. 9,268,053, and U.S.Publication No. 2017/0371063, all of which are assigned to the sameassignee, and hereby incorporated herein by reference in theirentireties.

Azimuthal resistivity measurement antennas use an electric coil togenerate an alternating current loop in the formation by induction. Thealternating current loop, in turn, induces a voltage signal in areceiving coil located elsewhere in the tool. The voltage signal inducedin the receiving coil is related to a parameter of the formation.Multiple transmitting and receiving coils may be used to focus formationcurrent loops both radially (depth of investigation) and axially(vertical resolution).

As used herein in reference to antennas, “transverse” refers to amagnetic moment, created by electrical current in a wire loop, having adirection orthogonal or substantially orthogonal relative to alongitudinal axis of the tool body. “Axial” refers to a magnetic moment,created by electrical current in a wire loop, having a direction alignedor substantially aligned or parallel with a longitudinal axis of thetool body.

For frame of reference and as used herein, the Z-axis points along alongitudinal axis of the tool body. The X-axis falls in a gravity planecontaining the Z-axis. In a tool including transmitter and receiverantennas oriented in the X, Y, or Z directions, nine differentcombinations of transmitter and receiver antennas are possible: XX, XY,XZ, YX, YY, YZ, ZX, ZY, and ZZ, where the first letter indicates theorientation of the transmitter antenna and the second letter theorientation of the receiver antenna. Those combinations provide means toimage the formation around a borehole. In particular, the XZ, ZX, YZ,and ZY components or their combinations provide the most usefulazimuthal resistivity measurement for resolving an adjacent boundary orother geological features around a wellbore.

FIGS. 6A-6C illustrate embodiments of tool body 100 including atransverse receiving antenna 120 and an axial transmitting antenna 110.The axial transmitting antenna 110 may be placed in either the upholedirection or the downhole direction relative to the transverse receivingantenna 120. The receiving antenna 120 is spaced apart from thetransmitting antenna 110 at a predefined distance. The direction of themagnetic moment of the axial transmitting antenna 110 remainssubstantially unchanged as the measurement tool 100 rotates, whereasthat of the transverse receiving antenna 120 rotates with the tool 100.To make an azimuthal measurement, a current (e.g., alternating) isdriven to the axial transmitting antenna 110 (also known as firing theantenna) at moments controlled by a microcontroller (not shown) of thetool to transmit electromagnetic waves into the surrounding medium at aselected frequency. The transmitted signal, when encountering aresistivity boundary near the borehole, is reflected back and receivedby the transverse receiving antenna 120. The detected voltage signal isrecorded at one or more tool face angles as the tool rotates. Themeasurement tool includes a sensor 102 configured to measure the angularposition of the tool body relative to the wellbore (e.g., tool faceangles). For example, the sensor 102 may be an accelerometer, amagnetometer, a gyro, or any other known sensor or sensor combination.If multiple transverse receiving antennas are used, the reflectedelectromagnetic wave may be detected simultaneously by the receivingantennas.

FIG. 6B and 6C illustrate embodiments of a resistivity measuring tool100 including a transverse receiving antenna 120 and a pair ofsymmetrical (FIG. 1B) or asymmetrical (FIG. 1C) axial transmittingantennas 110. The pair of axial transmitting antennas 110 may beenergized sequentially or simultaneously as explained later. And asfurther discussed below, by combining and processing the signals due tothe two axial transmitting antennas, whether fired sequentially orsimultaneously, a formation resistivity anisotropy effect on theazimuthal measurement may be reduced or removed, leaving the processedresponse largely sensitive to an adjacent bed boundary. Alternatively,the signals generated by the two axial transmitting antennas 110 may beprocessed to remove or reduce the bed boundary effect and enhance theformation resistivity anisotropy effect.

FIGS. 7A and 7B illustrate an embodiment of a resistivity measuring tool100. Multiple transverse receiving antennas 120 are located around acircumference of the tool body 105 and separated by varying angles inthe azimuthal direction, preferably 90 degrees in the azimuthaldirection, although a different separation angle may also be used. Forexample, in certain embodiments, two transverse antennas may beseparated by at least about 30 degrees, at least about 45 degrees, or atleast about 60 degrees. Transverse receiving antennas are preferablylocated at substantially the same longitudinal position (e.g., along theZ-axis) on the tool axis but may be located at different longitudinalpositions as well. One or more axial transmitting antennas 110 arepreferably placed longitudinally on opposite sides of the receivingantenna(s) 120, although they may also be placed on the same side of thereceiving antenna(s) 120. When more than one axial transmitting antennas110 are used, they may be fired sequentially or simultaneously. Themeasured signals due to the two transmitting antennas 110 may beprocessed to either remove or enhance the formation resistivityanisotropy effect, discussed in greater detail below. The resistivitymeasuring tool having multiple transverse receiving antennasazimuthally-spaced around the tool body may be more preferably used tomeasure formation resistivity when the tool is slowly rotating or notrotating.

FIG. 8 illustrates an embodiment of transverse antenna components. Anantenna pocket 122 is formed (e.g., machined, molded, etc.) near anouter surface of a drill collar body 105. The pocket 122 extendsradially inward from the outer surface of the drill collar body to amaximum radial depth of one half a diameter of the tool body.Preferably, the pocket may be at least 0.25 inches deep, or up to 0.5inches deep, or up to about one inch deep, or deeper. The pocket 122 maybe any shape including square, rectangle, circle, ellipse or othershapes. In the case of a square or rectangle pocket, the corners of thepocket may be smoothed to reduce stress accumulation around the corners.An antenna body 124 is configured to substantially correspond in shapewith and to fit within the pocket 122. The antenna body 124 may be madeof any non-conducting material, including but not limited to as PEEK,fiberglass, or ceramic. An antenna wire 126 is wound around the antennabody 124 such that the wire 126 extends substantially along thelongitudinal direction (Z-axis) of the tool axis 101. One or multipleturns of wire may be wound around the antenna body 124. To help hold thewire in place, wire grooves 125 may be formed on the outer surface ofthe antenna body 124. The wire 126 may be insulated with Teflon or othernon-conducting material to prevent short-circuiting between turns andfrom being exposed to drilling fluids. The antenna body 126 with thewound antenna wire 125 is inserted into the antenna pocket 122 such thatthe moment of the antenna points in a transversal direction. The ends ofthe antenna wire 125 exit the antenna pocket 122 to a nearby pocket (notshown) formed in the collar body 105 where a preamplifier may be placedto amplify the received signal before the signal is fed to an electronicboard (not shown).

An antenna shield 128 may be placed over the antenna body 124 after itis inserted within the antenna pocket 122. Preferably, the antennashield is configured to sit flush with an outer surface of the collarbody 105. The antenna shield 128 may be made of the same material as thecollar body 105, or a different, preferably harder, material. In oneembodiment, the antenna shield and collar body may be made of stellite.One or more openings 130 may be formed in the antenna shield 128 toallow electromagnetic energy to pass through. The openings 130 arepreferably aligned in the azimuthal direction. The antenna shield 128may be attached to the collar body 105 either with bolts or by weldingor other means.

Non-conducting, abrasion-resistant materials, or potting material, maybe used to fill any remaining voids or cavities within the antennapocket 122, after the antenna body 124 is inserted and the antennashield 128 is attached, for further protection of the antenna wire 126.To increase the antenna efficiency, the potting material may be mixedwith magnetic materials so that the mixture has a relative magneticpermeability greater than 1. Such a transversal antenna may be referredto as an “elemental” transverse antenna. Because the shield openingsextend substantially along the circumferential direction, they may besubject to wear and tear during drilling. To help protect the pottingmaterial from being damaged or worn out, the shield openings may benarrow. To further protect the potting material, curved openings may beused instead of straight openings. Each curved opening is preferablysymmetric with respect to the center point of the opening.

FIGS. 9A-9D illustrate cross-section views of a collar body 105 having apair of transverse elemental antennas 120 combined to form a compositetransverse antenna. Any number of composite transverse antennaconfigurations may be formed. FIG. 4A illustrates an antenna body 124and antenna wire winding 126 within a pocket 122 and covered by anantenna shield 128, forming a transverse elemental antenna 120. Current“I” flows in the antenna wire winding 126 in a direction shown by thearrows to generate a transverse magnetic moment M_(T) substantiallyorthogonal to the tool body axis. FIG. 4B illustrates a pair oftransverse elemental antennas 120 disposed opposite each other on thecollar body 105 and connected to form a composite transverse antenna.The transverse elemental antennas 120 may be connected by a wire 121 ofany diameter that extends from one transverse antenna to the other. Theconnecting wire 121 may be disposed within the collar body 105 fordamage protection, for example, extending through a drilled hole in thecollar body 105 starting from one transverse elemental antenna 120 andending at the second transverse elemental antenna 120. Alternatively, agroove may be machined on an outer surface of the collar body 105, thewire 121 disposed within the groove running between the two transverseantennas, and the groove welded for mechanical protection. Yet othermeans of wire connection between two transverse elemental antennas arepossible. For instance, the wire from each transverse elemental antennamay exit directly to an adjacent electronics board for signalcommunication. In this case, the pair of transverse elemental antennasmay be connected indirectly through the electronics board. The pair oftransverse elemental antennas 120 may be connected or coupled indifferent ways to generate different combinations of transverse magneticmoments.

FIG. 9B illustrates transverse elemental antennas 120, with currents Iflowing in the antenna wire windings 126 in directions shown by thearrows, which generate transverse magnetic moments M_(T) in the sametransverse direction. In this configuration, the transverse antennamoments M_(T) may be additive to each other and the pair of transverseantennas 120 produce a composite transversal antenna with its effectivecenter on the tool axis. That is, the pair of elemental antennas shownin FIG. 4B are connected in series so that signals from each are addedto form a stronger signal (e.g., a composite transverse moment=2M_(T)).

FIG. 9C illustrates transverse elemental antennas 120, with currents Iflowing in the antenna wire windings 126 in direction shown by thearrows, which generate transverse magnetic moments M_(T) in oppositetransverse directions. A composite transverse antenna in thisconfiguration will not produce any significant transverse magneticmoment component (e.g., a composite transverse moment≈0). Rather, theresulting magnetic moments may resemble a quadrupole. An electricalcurrent flowing in the tool's longitudinal direction will produce amagnetic field circulating around the collar. The magnetic fields on theopposite sides of the collar will point to opposite azimuthal directionswhen viewed in a Cartesian coordinate system, which will produce aresponse in the quadrupole antenna.

FIG. 9D illustrates transverse elemental antennas 120, with currents Iflowing in the antenna wire windings 126 in directions shown by thearrows, which generate transverse magnetic moments M_(T) in the sametransverse direction, similar to FIG. 4B. However, the antennas shown inFIG. 4D are electrically connected in parallel. Therefore, transversemagnetic moments M_(T) are not added (e.g., a composite transversemoment=M_(T)), however if one antenna fails the other still provides thesame signal strength. That is, transverse elemental antennaselectrically connected in parallel provide redundancy in case oneantenna fails, the composite antenna will still have the same moment asif there was no failure.

FIG. 10 illustrates an embodiment of axial antenna components. Anantenna groove 112 may be formed in an outer surface of the tool body105. The width of the antenna groove 112 may be at least one-half inchor up to eight inches or greater, but preferably between one inch andsix inches measured along the longitudinal direction of the collar. Adepth of the antenna groove 112 may be at least 0.05 inches, at least0.1 inches, at least 0.25 inches, at least 0.5 inches, at least oneinch, or greater. A wire groove 114 may be formed in an outer surfaceand near the center of the antenna groove 112. The wire groove 114should be wide and deep enough to hold one or multiple turns of antennawire 115. Individual wire ways may also be created to hold each turn ofwire in place. Longitudinal slots 116 may be formed in an outer surfaceof the antenna groove 112 for passage of electromagnetic wave energy,and may be referred to as passage slots. The passage slots 116 may be atleast 0.25 inches deep, or at least 0.5 inches deep, or at least oneinch deep, depending on the size of the collar. The passage slots 116may be separated from each other by at least approximately 0.25 inches,or at least 0.5 inches, or at least one inch, or at least two inches, orgreater. One or multiple turns of antenna wire 115 may be disposed inthe wire groove 114. The antenna wire 115 may exit the antenna groovethrough pressure sealed connectors to a pressure-sealed pocket (notshown) near the antenna groove 112.

An antenna shield 118 may be placed on top of the antenna groove 112 tocover the antenna wire. The antenna shield 118 may be made of the samematerial as the collar body 105 or a different, preferably harder,material (e.g., stellite) to protect the antenna wire from being damagedduring drilling. The antenna shield 118 may include two or morecylindrical pieces, each having multiple slots 119 formed within. Theshield slots 119 may be aligned with the passage slots 116 formed in theantenna groove 112. The shield slots 119 may be at least 0.05 incheswide, or at least 0.1 inches wide, or at least 0.5 inches wide, or atleast one inch wide, but are preferably within 0.1 to 0.5 inches wideand do not have to be the same width as the underneath passage slots.The thickness of the shield may be at least 0.05 inches, or at least 0.1inch, or at least 0.25 inches, or at least 0.5 inches, or at least oneinch, or greater. The shield 118 may be secured or locked to the collarbody 105 either through welding or by bolts. Further, the antenna bodymay be vacuumed and potted with non-conducting material for integrityand damage protection. The surface of the antenna may be polished toremove any outstanding material.

FIGS. 11A-11C illustrate embodiments of co-located antennas in the drillcollar body. FIG. 6A illustrates an embodiment of co-located transverseantennas, each including a pair of transverse elemental antennas 120connected as discussed in reference to FIGS. 4A-D. The pairs oftransverse antennas generate magnetic moments M_(T) in the samedirection, although any of the composite transverse antenna arrangementsmay be configured. Connecting wires 121 and wire ways between the pairsof transverse elemental antennas 120 preferably do not intercept, andeach transverse elemental antenna 120 transmits or receiveselectromagnetic energy independently. FIG. 6B illustrates an embodimentof co-located transverse elemental antennas 120 and axial antennas 110.The pair of transverse antennas 120 generate magnetic moments M_(T) inthe same direction, although any of the composite transverse antennaarrangements may be configured. The pair of axial antennas 110 generatemagnetic moments MA in either direction. The axial antenna 110 includestwo axial elemental antennas spaced apart by 180 degrees in theazimuthal direction and connected by a wire way for wire passage 121.The wire ways preferably do not intercept each other. In certaininstances, the axial antenna may include a single axial antenna, inwhich case no wire way will be needed.

Various methods of making azimuthal resistivity measurements with andwithout tool rotation are disclosed. One purpose of azimuthalresistivity measurements is generating information for resolution of theazimuthal direction of and distance to an adjacent boundary near thewellbore. This may be accomplished with one axial transmitting antennaand one elemental transversal receiving antenna. While the transmittingantenna is firing, a signal is acquired from the receiving antenna asthe tool rotates. In the presence of a bed boundary near the wellboreand assuming that the boundary is azimuthally located at a tool faceangle of ϕ₀, the signal measured will vary with tool face angle as:

A(ϕ)=A ₀ cos(ϕ+ϕ₀)   (1)

where A₀ is the maximum (in the absolute value) value of the azimuthalsignal when the transversal receiver antenna points toward the boundary,i.e., at the tool face angle ϕ₀ and ϕ is tool face angle. In equation(1), A₀ depends on the resistivities of both the near and the remotebeds, distance to the boundary, coil spacing, frequency, antennamoments, and the driving current in the transmitting antenna. Solvingequation (1) for A₀ and ϕ₀ requires at least two independentmeasurements, which may be accomplished by taking measurements at two ormore distinct tool face angles. It may be expressed as:

$\begin{matrix}{A_{1} = {{A_{0}\mspace{14mu} {\cos ( {\varphi_{1} + \varphi_{0}} )}} + e_{1}}} & (2) \\{A_{2} = {{A_{0}\mspace{14mu} {\cos ( {\varphi_{2} + \varphi_{0}} )}} + e_{2}}} & (3) \\\ldots & \; \\{A_{n} = {{A_{0}\mspace{14mu} {\cos ( {\varphi_{n} + \varphi_{0}} )}} + e_{n}}} & (4)\end{matrix}$

In equations (2)-(4), e₁, e₂, . . . e_(n) are measurement errors, andthe equations may be solved in the least-square sense which is wellknown.

In the case where the tool does not rotate, multiple transverse antennasare used to generate independent measurements at different tool faceangles. For example, two transverse elemental antennas separated by 90degrees in the azimuthal direction, may be used. They are preferablylocated at the same longitudinal position on the tool axis but this isnot necessary. Measurements from each antenna may be written as:

A ₁ =A ₀ cos(ϕ₁+ϕ₀)+e ₁   (5)

A ₂ =A ₀ cos(ϕ₁+90+ϕ₀)+e ₂ =A ₀ sin(ϕ₁+ϕ₀)+e ₂   (6)

Equations (5)-(6) may be solved for A₀ and ϕ₀ using a least squaresmethods. Here, in a cross-section view, the magnetic moments generatedby the two transversal antennas are assumed to be orthogonal to eachother, although not necessary. In general, the two transverse elementalantennas may be separated in the azimuthal direction by any anglebetween 0° and 360°. In this case, equations (5)-(6) becomes:

A ₁ =A ₀ cos(ϕ₁+ϕ₀)+e ₁   (7)

A ₂ =A ₀ cos(ϕ₁+ϕ+ϕ₀)+e ₂   (8)

where z is the azimuthal angle separation between the two antennas.

For the special case of equations (5)-(6) and in the absence ofmeasurement noises, both A₀ and ϕ₀ may be computed as:

$\begin{matrix}{A_{0} = ( {A_{1}^{2} + A_{2}^{2}} )^{1\text{/}2}} & (9) \\{\varphi_{0} = {\tan^{- 1}( \frac{A_{2}}{A_{1}} )}} & (10)\end{matrix}$

For the general case of equations (7)-(8), inversion must be applied tocompute A₀ and ϕ₀.

If multiple transverse elemental antennas are used that are located atsubstantially the same longitudinal position on the tool axis, it ispossible to form a virtual transversal antenna by combining the multipletransversal antennas. The combination may be done either by electricallyconnecting the antennas together or by adding their responses together,examples of which were discussed in reference to FIGS. 4A-D. Forinstance, if two transverse elemental antennas are separated by anazimuthal angle Δϕ, then their combined response:

A=A ₁ cos(ϕ+ϕ₀)+A ₂ cos(ϕ+Δϕ+ϕ₀)=B cos(ϕ+ϕ′)   (11)

is another cosine function of the tool face angle. In the above,

$\begin{matrix}{B = ( {A_{1}^{2} + A_{2}^{2} + {2A_{1}A_{2}\mspace{14mu} \cos \mspace{14mu} {\Delta\varphi}}} )^{1\text{/}2}} & (12) \\{\varphi^{\prime} = {\tan^{- 1}( \frac{{A_{1}\mspace{14mu} \sin \mspace{14mu} \varphi_{0}} + {A_{2}\mspace{14mu} {\sin ( {\varphi_{0} + {\Delta\varphi}} )}}}{{A_{1}\mspace{14mu} \cos \mspace{14mu} \varphi_{0}} + {A_{2}\mspace{14mu} {\cos ( {\varphi_{0} + {\Delta\varphi}} )}}} )}} & (13)\end{matrix}$

Advantageously, combined antennas or signals over individual antennas orsignals may lead to better noise rejection and improved signal-to-noiseratios. And, if one of the antennas fails, the combined signal willstill be usable.

Signals from multiple transverse elemental receiving antennas may beacquired simultaneously when a transmitting antenna fires. The signalsmay also be acquired sequentially as a transmitting antenna fires,regardless of tool rotation. The tool face angle will be recorded by asensor while recording the signals. The signals are associated with thetool face measurements in computing a formation parameter of interest.When the tool rotates, measurements from two transverse (e.g., X and Y)elemental receiving antennas as a function of tool face angle willresemble each other, which provides data redundancy. Combining a largerset of measurements may be used for subsequent processing andinterpretation, while independently processing measurements from eachtransverse elemental antenna may be used for quality control purposes,among others.

Cross-component antenna arrangements (e.g., an axial transmittingantenna and a transverse elemental receiving antenna) disclosed hereinmay be used for making azimuthal resistivity measurements for detectionand resolution of an adjacent bed boundary in a formation. However,detection and resolution of adjacent bed boundaries using suchcross-component antenna arrangements may oftentimes be affected byformation resistivity anisotropy (e.g., directionally dependentformation properties). That is, formation resistivity anisotropy mayproduce an anomalous signal similar to that produced by an adjacent bedboundary. The cross-component response to an anisotropic formation maybe written as:

$\begin{matrix}{V_{zx} = {\frac{M_{T}M_{R}I}{4\pi \; L^{3}}\lbrack {\frac{\cos \mspace{14mu} \theta}{\sin \mspace{14mu} \theta}{ik}_{h}{L( {e^{{ik}_{h}L} - e^{{ik}_{h}\beta \; L}} )}} \rbrack}} & (14)\end{matrix}$

Where:

$\begin{matrix}{{k_{h} = ( {i\; {\omega\mu\sigma}_{h}} )^{1\text{/}2}}{\beta = ( {{\cos^{2}\mspace{14mu} \theta} + {\frac{R_{h}}{R_{v}}\sin^{2}\mspace{14mu} \theta}} )^{1\text{/}2}}} & (15)\end{matrix}$

In the above equation, M_(T) and M_(R) are the effective areas of thetransmitting and receiving antennas, respectively, I is the drivingcurrent in the transmitting antenna, and θ is the relative dip angle ofthe formation relative to the tool axis. If the resistivity anisotropyis produced by lamination of thin beds of different resistivity values,the relative dip angle θ will be 90 degrees if the wellbore (or toolaxis) is parallel to the bedding planes. V_(zx) will be nonzero as longas the relative dip angle θ is different from 0 or 90 degrees. Asdetermined from equation (14), the cross-component signal V_(zx) willremain the same if the relative dip angle changes by 180 degrees.Therefore, an axial transmitting antenna located longitudinally on oneside of the receiving antenna will produce the same response as if thetransmitting antenna is moved to the other side of the receiving antennaat a symmetrical position and driven with the same driving current.Hence, a signal response due to an anisotropic formation may be removedby subtracting the responses generated by two longitudinally symmetricaltransmitting antennas. In contrast, the responses produced at anadjacent bed boundary due to two longitudinally symmetrical transmittingantennas will have opposite signs if the axial magnetic moments of thetransmitting antennas point in the same longitudinally direction. Hence,subtracting the two responses from each other will enhance the bedboundary response.

A method of data acquisition is disclosed for suppressing certainformation parameters while amplifying others, which includes firing twotransmitting antennas at least substantially simultaneously. Currentsmay be driven simultaneously to two transmitting antennas for generatingaxial magnetic moments in opposite directions, thereby inducing avoltage signal in the wire winding of the receiving antenna related to aparameter of an adjacent formation bed boundary (and reducing orcancelling the formation resistivity anisotropy effect). Alternatively,currents may be driven simultaneously to two transmitting antennas forgenerating axial magnetic moments in the same direction, therebyinducing a voltage signal in the wire winding of the receiving antennarelated to a parameter of formation resistivity anisotropy (and reducingor cancelling the bed boundary effect).

Simultaneously driving currents to the two transmitting antennasproduces a stronger signal and greater signal-to-noise ratio (SNR) thansequentially driving currents to transmitting antennas at the same powerinput. As an example, for total data acquisition time of T, and V₀indicating the voltage signal detected by a receiving antenna for a unitdriving current in a transmitting antenna, the power consumption by thetransmitting antenna may be written as:

P=I²R   (16)

where R is the total resistance of the antenna, i.e., the sum of theantenna wire resistance and the antenna radiation resistance. Noise inthe received signal may be assumed to be random and stacking of datawill result in reduction in noise according to:

n=cn ₀ /√{square root over (t)}  (17)

where n₀ is the noise level without any stacking, t is the acquisitiontime, and c is a proportionality constant. For sequential acquisition,the signal level is calculated by:

$\begin{matrix}{V_{1} = {V_{0}\sqrt{\frac{P}{R}}}} & (18)\end{matrix}$

Combining the two sequential measurements will result in asignal-to-noise (SNR) ratio for the combined signal calculated by:

$\begin{matrix}{{SNR}_{1} = \frac{V_{0}\sqrt{{PT}\text{/}R}}{{cn}_{0}}} & (19)\end{matrix}$

Similarly, for simultaneous acquisition, the total signal level iscalculated by:

$\begin{matrix}{V_{1} = {V_{0}\sqrt{\frac{2P}{R}}}} & (20)\end{matrix}$

The corresponding SNR is calculated by:

$\begin{matrix}{{SNR}_{2} = {\frac{V_{0}\sqrt{2{PT}\text{/}R}}{{cn}_{0}} = {\sqrt{2}{SNR}_{1}}}} & (21)\end{matrix}$

As shown, the SNR for simultaneous acquisition is increased by a factorof √{square root over (2)} over sequential acquisition for the sameinput power. After binning the measurements made at multiple tool faceangles into a number of sectors, the SNR for each sector will be lessthan that for the entire data combined. However, the relative gain inthe SNR for each sector with simultaneous acquisition will remain thesame as compared to sequential acquisition. In simultaneous acquisition,the two antennas preferably have the same effective cross-sectional areaand are driven with currents of the same magnitude. If they havedifferent effective cross-sectional areas, the driving currents thenmust be adjusted such that the products of the effective cross-sectionalarea and the driving current are the same.

In the above discussion, the two transmitting antennas are substantiallyequally spaced apart from the receiving antenna(s). In instances wherethe two transmitting antennas have different spacings from the receivingantenna(s), additional methods for compensating for formation anisotropyeffect are disclosed. In a first method, the two signals may bemeasured, with either sequential data acquisition or simultaneous dataacquisition, and subtracted. Subtracting the signals may work if thecoil spacing is small. As an example, coil spacing may be less than teninches or less than twenty inches. In other examples, coil spacing maybe twenty inches or greater. FIG. 7 illustrates a graph 700 showingsignal responses due to an anisotropic formation, an uncompensatedsignal response 702 and compensated signal response 704 using the firstmethod. The parameters are: Rh=1 ohmm, Rv=5 ohmm, θ=100°, L₁=40 in.,L₂=38 in., and f=2 MHz. The compensated signal is defined as:

V _(zx) ^(Comp)=1/2(V _(zx1) −V _(zx2))   (22)

A coefficient of ½ is included so that after the compensation the bedboundary response remains the same (if the bed boundary is parallel tothe tool axis). As shown, the first compensation method reduces theanisotropy effect by a factor of approximately 9.1, which represents agreat reduction in the anisotropy effect.

In a second method, equation (22) is corrected by adjusting the scalingfactor L (see equation (14)) to further compensate for the formationanisotropy effect. The two individual signals may be combined as followsto produce a new compensated signal:

$\begin{matrix}{V_{zx}^{Comp} = {\frac{1}{L_{1}^{3} + L_{2}^{3}}( {{V_{{zx}\; 1}L_{1}^{3}} - {V_{{zx}\; 2}L_{2}^{3}}} )}} & (23)\end{matrix}$

As shown, equation (23) reduces to equation (22) if L₁=L₂. FIG. 8illustrates a graph 800 showing signal responses due to an anisotropicformation, an uncompensated signal response 802 and compensated signalresponse 804 using the second method according to equation (23). Thesecond compensation method reduces the anisotropy effect by a factor ofapproximately 16.3, nearly doubling that of the first compensationmethod. Equation (23) may also be implemented for simultaneous dataacquisition. To do so, the currents in the two transmitter antennas arescaled by factors of L₁ ³/(L₁ ³+L₂ ³) and L₂ ³/(L₁ ³+L₂ ³),respectively.

In a third method, the anisotropy effect is directly removed from signalmeasurements by numerically computing the anisotropy effect usingequation (14). In the equation, the two unknown parameters Rh and β maybe calculated from the propagation resistivity measurements. Therelative dip angle θ must be input from other sources, e.g., the welldeviation angle and the known formation dip angle.

Referring back to FIG. 4b , the RSS housing (14) also encloses anazimuthal resistivity measurement antenna electronics (21), alsoreferred to herein as “measurement electronics.” The measurementelectronics (21) control and operate the azimuthal resistivity antennas(15)-(17) for making measurements of the surrounding formation,including measuring the distance to upper or lower formation boundaries.The RSS housing (14) also encloses azimuthal resistivity measurementantenna tuning electronics (22) that are configured to condition antennasignals to make sure the antennas are measuring properly, e.g.,calibration.

The RSS housing (14) also encloses a control module (18). The controlmodule (18) may be any type of microprocessor unit (“MPU”) whichincorporates the functions of all central processing for the rotarysteerable system on a single integrated circuit (“IC”), or at most a fewintegrated circuits. The control module (18) may be a multipurpose,clock driven, register based, digital-integrated circuit which acceptsbinary data as input, processes it according to instructions stored inits memory, and provides results as output.

The control module (18) is configured to execute a pre-programmed welltrajectory, e.g., a “well plan”. For example, the control module (18) isconfigured to execute a pre-programmed well trajectory, which includesazimuth (or direction) and total vertical depth (“TVD”), which isreferred to as a “geometric setting.” In addition, the control module(18) is pre-programmed to maintain a certain or desired distance from aformation boundary above or below the rotary steerable system, which isreferred to as a “boundary tracking setting.” That is, the controlmodule (18) is configured to control a vertical component of thethree-dimensional well path to avoid exiting from the formation, or adesired portion of the formation, either through a top or bottom of theformation. To do so, the azimuthal measurement antennas (15)-(17) “trackthe boundaries” for the formation above or below. Upon detecting thatthe rotary steerable system is about to exit through a formationboundary, or is too close to a formation boundary (e.g., less than acertain or desired distance), the control module (18) corrects therotary steerable system path.

Accordingly, once the geometric and boundary tracking settings arepre-programmed, the control module (18) acts autonomously in respondingto the changing geology of a formation, much like a self-drivingvehicle. As the rotary steerable system is travelling along apre-programmed three-dimensional well path, the azimuthal resistivitymeasurement antennas (15)-(17) are measuring its distance from formationboundaries above or below, and based on the measurements, the controlmodule (18) is determining whether correction up or down is needed toavoid exiting the formation. Thus, the control module (18) steers therotary steerable system to stay within the producing formation and/orreach a pre-determined target or location in the formation.

Boundary tracking data may be based on a tool face (“TF”) angle obtainedby the control module (18). In certain embodiments, if the azimuthalresistivity measurement antennas (15)-(17) require their own tool facesampling, the tool face angle at the control module (18) may becorrected by entering an angle value for the radial offset between thecontrol module (18) and the measurement electronics (21). The controlmodule (18) is configured to measure TF angle and, if necessary, to makecorrections to inclination or azimuth. The control module (18) isconfigured to communicate with the pulser/battery/electromagnetic (“EM”)transmitter (4) and/or the MWD tool (6), In certain embodiments, thecontrol module (18) and the measurement electronics (21) may be axiallyaligned to avoid making a tool face offset correction. For example, thecontrol module (18) and the measurement electronics (21) may be hardmounted on the same platform within the non-rotating RSS (14) such thatthey are axially aligned.

Advantageously, embodiments disclosed herein provide a rotary steerablesystem that has a control module directly integrated inside thenon-rotating rotary steerable housing for precisely steering the rotarysteerable system through a formation and between boundaries. The housinghas the azimuthal resistivity measurement antennas integrated thereinand the control module measures the distance to the formation boundary(either upper or lower) and operates the antennas to operateautonomously and thereby maintain a certain distance from upper andlower boundaries of a formation. Further, measurements are performedright behind the bit for improved precision and accuracy. The controlmodule eliminates the need for a logging-while-drilling (“LWD”) stringwith separate azimuthal resistivity measurement tools, whichconsiderably shortens the length of the RSS bottom hole assembly.Overall reliability of the rotary steerable bottom hole assembly.

One or more embodiments disclosed herein are for a rotary steerablebottom hole assembly comprising a drill bit disposed at a distal endthereof, a stabilizer disposed in the bottom hole assembly uphole fromthe drill bit, and a non-rotating steerable housing disposed between thestabilizer and the drill bit. The non-rotating steerable housingincludes azimuthal resistivity antennas and electronics configured tomeasure a distance to an approaching formation boundary. Thenon-rotating steerable housing further includes a control moduleconfigured to steer the drill bit along a well path and, based onmeasurements from the azimuthal resistivity antennas, to steer thehousing away from the approaching formation boundary and therebymaintain a certain distance between the steerable housing and upper orlower boundaries of a formation.

Embodiments disclosed herein may include a rotary steerable bottom holeassembly wherein the non-rotating housing further encloses a hydraulicpump and pump drive for operating one or more rams to steer the drillbit.

Embodiments disclosed herein may include a rotary steerable bottom holeassembly wherein the control module is configured to execute apre-programmed well trajectory.

Embodiments disclosed herein may include may include a rotary steerablebottom hole assembly wherein the control module is configured to controla vertical component of the well path.

One or more embodiments disclosed herein may include a rotary steerablesystem comprising a non-rotating housing, azimuthal resistivity antennasand electronics, disposed within the non-rotating housing, configured tomeasure a distance to an approaching upper or lower formation boundary,and a control module configured to steer a drill bit along a well pathand, based on measurements from the azimuthal resistivity antennas, tosteer the housing away from the approaching upper or lower formationboundary and thereby maintain a certain distance between the steerablehousing and upper or lower formation boundary.

Embodiments disclosed herein may include a rotary steerable system,further comprising a hydraulic pump and pump drive for operating one ormore rams to steer the rotary steerable system.

Embodiments disclosed herein may include a rotary steerable systemwherein the control module is configured to execute a pre-programmedwell trajectory.

Embodiments disclosed herein may include a rotary steerable systemwherein the non-rotating housing is disposed between the drill bit and astabilizer.

Embodiments disclosed herein may include a rotary steerable systemwherein the control module is configured to control a vertical componentof the well path.

One or more embodiments disclosed herein may include a method ofdirectional drilling comprising steering a drill bit along a well pathby operating a rotary steerable system having a control module enclosedwithin a non-rotating steerable housing, measuring a distance betweenthe steerable housing and a distance to an approaching upper or lowerformation boundary with azimuthal resistivity antennas disposed withinthe non-rotating steerable housing, and steering the drill bit away fromthe approaching upper or lower formation boundary, based on theazimuthal resistivity measurements, to maintain a certain distancebetween the steerable housing and the approaching upper or lowerboundary of the formation.

Embodiments disclosed herein may include a method of directionaldrilling, further comprising steering the drill bit by radiallyextending one or more rams disposed within the non-rotating housingoutward to press against the wellbore thereby causing the drill bit topress on an opposite side of the wellbore and cause a direction change.

Embodiments disclosed herein may include a method of directionaldrilling wherein the control module is configured to execute apre-programmed well trajectory.

Embodiments disclosed herein may include a method of directionaldrilling, wherein the control module is configured to control a verticalcomponent of the well path.

The claimed subject matter is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described herein will become apparent tothose skilled in the art from the foregoing description. Suchmodifications are intended to fall within the scope of the appendedclaims.

What is claimed is:
 1. A rotary steerable bottom hole assemblycomprising: a drill bit disposed at a distal end thereof; azimuthalresistivity antennas comprising: an axial antenna including a wire forgenerating an axial magnetic moment substantially aligned with thelongitudinal axis; a transverse antenna including an antenna body havinga longer axis disposed longitudinally in the housing, and a wire coilhaving a central axis disposed around the antenna body, wherein the wirecoil central axis is substantially perpendicular to the longer axis ofthe antenna body, and wherein the wire coil is configured to generate atransverse magnetic moment orthogonal to the housing longitudinal axis.2. The rotary steerable bottom hole assembly of claim 1, furthercomprising a stabilizer disposed in the bottom hole assembly uphole fromthe drill bit.
 3. The rotary steerable bottom hole assembly of claim 2,further comprising a steerable housing having a longitudinal axis anddisposed between the stabilizer and the drill bit, wherein the azimuthalresistivity antennas are in the housing.
 4. The rotary steerable bottomhole assembly of claim 3, further comprising a control module in thehousing configured to steer the drill bit along a well path and, basedon measurements from the azimuthal resistivity antennas, to steer thehousing and maintain a distance between the housing and the formationboundary.
 5. The rotary steerable bottom hole assembly of claim 4,wherein the housing further encloses a hydraulic pump and pump drive foroperating one or more rams to steer the drill bit.
 6. The rotarysteerable bottom hole assembly of claim 4, wherein the control module isconfigured to execute a pre-programmed well trajectory.
 7. The rotarysteerable bottom hole assembly of claim 4, wherein the control module isconfigured to control a component of the well path.
 8. A rotarysteerable system comprising: azimuthal resistivity antennas, theazimuthal resistivity antennas comprising: an axial antenna including awire for generating an axial magnetic moment substantially aligned withthe longitudinal axis; a transverse antenna including an antenna bodyhaving a longer axis disposed longitudinally in the housing, and a wirecoil having a central axis disposed around the antenna body, wherein thewire coil central axis is substantially perpendicular to the longer axisof the antenna body, and wherein the wire coil is configured to generatea transverse magnetic moment orthogonal to the housing longitudinalaxis.
 9. The rotary steerable system of claim 8, further comprising ahousing in which at least one of the azimuthal resistivity antennas areenclosed.
 10. The rotary steerable system of claim 9, further comprisinga control module in the housing configured to steer a drill bit along awell path and, based on measurements from the azimuthal resistivityantennas, to steer the housing to maintain a distance between thesteerable housing and the formation boundary.
 11. The rotary steerablesystem of claim 10, further comprising a hydraulic pump and pump drivein the housing for operating one or more rams to steer the rotarysteerable system.
 12. The rotary steerable system of claim 10, whereinthe control module is configured to execute a pre-programmed welltrajectory.
 13. The rotary steerable system of claim 10, wherein thehousing is disposed between the drill bit and a stabilizer.
 14. Therotary steerable system of claim 10, wherein the control module isconfigured to control a component of the well path.
 15. A method ofdrilling comprising: measuring a distance with azimuthal resistivityantennas comprising: an axial antenna including a wire for generating anaxial magnetic moment substantially aligned with the longitudinal axis;and a transverse antenna including an antenna body disposedlongitudinally in the housing, and a wire coil having a central axisdisposed around the antenna body, wherein the wire coil central axis issubstantially perpendicular to the longer axis of the antenna body, andwherein the wire coil is configured to generate a transverse magneticmoment orthogonal to the housing longitudinal axis.
 16. The method ofclaim 15, further comprising steering a drill bit along a well path byoperating a rotary steerable system having the azimuthal resistivityantennas and a control module enclosed within a steerable housing. 17.The method of claim 16, further comprising steering the drill bit, basedon the azimuthal resistivity measurements, to maintain a distancebetween the antennas and the formation boundary.
 18. The method of claim17, further comprising steering the drill bit by radially extending oneor more rams disposed within the housing outward to press against thewellbore thereby causing the drill bit to press on an opposite side ofthe wellbore and cause a direction change.
 19. The method of claim 17,wherein the control module is configured to execute a pre-programmedwell trajectory.
 20. The method of claim 17, wherein the control moduleis configured to control a component of the well path based on themeasured distance.